The present invention relates generally to aircraft safety systems, and more specifically to a catapult which provides controllable acceleration to an aircraft ejection seat.
An ejection seat catapult propels the ejection seat out of an aircraft cockpit during an emergency ejection. Conventional catapults are pneumatic piston/cylinder devices, pressurized by hot gas generated by burning a solid propellant grain. The fixed performance capabilities of open loop catapults are not satisfactory for some ejection conditions encountered in today's military aircraft. Variations in propellant temperature of -65.degree. F. to +160.degree. F. (required operating range of ejection seat subsystems) result in a variation in catapult thrust levels of approximately 25%. This variation together with variations of the ejected weight produce a large variation in impressed Gs on the crewmember during catapult operation. If catapult thrust is low and the ejected weight is high, the ejection velocity and trajectory height will be affected. If catapult thrust is high and the ejected weight is low, the resultant accelerations could cause injury to the crewmember. Ejection in a "G field" --that is while the aircraft is in a maneuver which loads the crewmember in the spinal axis--further increases the potential for ejection force injury.
When an ejection seat/airman combination is ejected from an aircraft in an exergency it is desireable that this combination hould attain a high velocity in predetermined direction in as hort a time as possible consistent with the application of physiologically acceptable acceleration values to the airman. It is important that the trajectory of the seat/aircraft combination should be such that the combinations will adequately clear all parts of the aircraft in any flight condition. It is also important that the combination should have sufficient time for the deployment and effective operation of the crewmember's parachute.
The task of providing an aircraft seat ejection system which possesses controllable acceleration is alleviated to some extent, by the following U.S. patents, the disclosures of which are incorporated by reference:
U.S. Pat. No. 3,027,125 issued to Fulton; PA1 U.S. Pat. No. 3,124,324 issued to Martin; PA1 U.S. Pat. No. 3,355,127 issued to Stanley et al; PA1 U.S. Pat. No. 3,688,636 issued to Spiess et al; PA1 U.S. Pat. No. 4,396,171 issued to Schultz; and PA1 U.S. Pat. No. 4,505,444 issued to Martin.
The patent of Fulton describes the problems associated with a single propellant catapult and proposes the use of a large numter of explosive charges spaced along the tube to be ignited successively as the piston moves down the tube. The acceleration of the seat, is, however, not monitored or controlled.
The patent of Martin uses a plurality of rockets with selected thrust direction to cause the pilot and seat to travel in a desired direction. The acceleration of the seat is not monitored or controlled.
The reference Stanley describes the use of a flexible tow line assembly attached to the pilot and carried aloft by a rocket to pull the pilot from the aircraft when it becomes taut. It has no control over acceleration.
The patent of Spiess et al provides for presetting the thrust of the ejector to control the height the seat reahes when ejected but cannot vary the thrust during ejection.
The Schultz disclosure differs from the references described above, in that it provides for controlling acceleraton of the seat and pilot during ejection. It uses an electronic controller to sense acceleration and, if too high, vent the gas from the catapult, but it cannot increase acceleration if too low, as presently required.
From the foregoing discussion, it is apparent that there currently remains a need for a controllable seat ejection catapult which is capable of increasing and decreasing the seat acceleration to preserve the safety of an aircraft crewmember during emergencies. The present invention is intended to satisfy that need.